Network ink jet printers use high carriage velocities and high acceleration rates to achieve printing at rates of over 10 pages per minute. To minimize the mass that must be accelerated, ink reservoirs are usually located off-board the carriage and various systems are implemented to transfer ink from the reservoirs to the printhead cartridges.
U.S. Pat. No. 5,369,429 employs a continuous ink supply system wherein flexible hoses or tubes connect a plurality of printhead cartridges to respective ones of a plurality of off-board ink reservoirs so that ink is supplied continuously to the cartridges as needed. U.S. Pat. Nos. 3,967,286, 4,967,207, 4,968,998 and 5,136,305 disclose intermittent ink supply systems wherein an ink jet cartridge is intermittently filled from an off-board reservoir by moving the cartridge to a service station where the reservoir is located.
The intermittent and continuous ink supply systems of the prior art share a common disadvantage when employed in color network printers. Because (1) ink is consumed relatively rapidly due to the high printing rates, (2) there are four or possibly six colors of ink being used, and (3) the ink supply for each color is an undivided ink supply, an operator must intervene in the printing process relatively frequently to replenish the off-board ink supplies, thus reducing the time the printer is available for printing. For example, in a printer capable of printing in four colors, and having an undivided off-board supply for each color holding enough ink for printing 20,000 prints or pages (5% coverage), an operator has to intervene in the printing process, on average, about every 5000 prints because the different colors of ink are not used up at the same time. In the worst case, a second intervention may be required only one page after a first intervention. This assumes that only the empty ink supply is replaced during an intervention. Of course all the reservoirs could be replaced during a given intervention but this would be wasteful of ink and increase the printing costs.